Overclocking could be a major issue as it is almost pointless to overclock a graphics card because in the end you will only get a couple more fps's, if you can restore the graphics cards setting back to default like the overclock settings. Overclocking a GPU isn't like overclocking a CPU as a CPU is easier to make stable and GPU's are very hard to make stable so try to restore the overclock setting and the 670 is alreadys a best card why overclock it.